Kinetic and Binding Studies Reveal Cooperativity and Off‐Cycle Competition for H‐Bonding Catalysis with Silsesquioxane Silanols

Abstract

The catalytic activity, kinetics, and quantification of H‐bonding ability of incompletely condensed polyhedral oligomeric silsesquioxane (POSS) silanols are reported. POSS‐triols, a homogeneous model for vicinal silica surface sites, exhibit enhanced H‐bonding compared with other silanols and alcohols as quantified using a 31P NMR probe. Evaluation of a Friedel–Crafts addition reaction shows that phenyl‐POSS‐triol is active as an H‐bond donor catalyst whereas other POSS silanols studied are not. An in‐depth kinetic study (using RPKA and VTNA) highlights the concentration‐dependent H‐bonding behavior of POSS‐triols, which is attributed to intermolecular association forming an off‐cycle dimeric species. Binding constants provide additional support for reduced H‐bond ability at higher concentrations, which is attributed to competitive association. POSS‐triol self‐association disrupts H‐bond donor abilities relevant for catalysis by reducing the concentration of active monomeric catalyst.

NMR Quantification of Halogen-Bonding Ability To Evaluate Catalyst Activity

“…31 P NMR spectroscopy has been successfully applied to quantify noncovalent interactions upon binding to triethylphosphine oxide (TEPO) as a Lewis basic probe. − First reported by Gutmann and Beckett to measure Lewis acidic solvents, we and others have since adapted this method to quantify the H-bonding ability and Lewis acidity of various catalysts. , Previous work in our group has successfully demonstrated the proportional relationship of H-bonding ability and catalytic activity for a variety of H-bonding donors using 31 P NMR spectroscopy (Figure D) . Compared to the extensive application for H-bonding, the investigation of X-bonding ability for organocatalysts is limited. , Here, we report using the 31 P NMR spectroscopy method to systematically quantify X-bonding ability and correlate the catalytic ability for XBD organocatalysts (Figure E).…”

Acetone Factor in the Design of Cu4-, Cu6-, and Cu9-Based Cage Coppersilsesquioxanes: Synthesis, Structural Features, and Catalytic Functionalization of Alkanes

“…The investigation of partly condensed POSS is also appealing, leading to the design of new monomers for copolymerization reactions, H-bond donor catalysts, OLED’s emission layers, three-dimensional emulsifiers, different films (e.g., transparent, scratch resistant, self-healing, or Langmuir–Blodgett/Langmuir–Schaefer films), and spin-on-glass networks with ultralow dielectric constants . By design, partly condensed polyhedral silsesquioxanes can be also regarded as versatile ligands for the construction of various cagelike metallacomplexes. − These intriguing compounds attract significant interest for the potential removal of radioactive elements, fabrication of flame retardants, − biomedical agents, luminescent materials, , or molecular magnets .…”

Anion recognition by silanetriol in acetonitrile

“…It should be mentioned that silanol derivatives including silanediols have recently been utilized as organocatalysts by stabilizing the transition state of various organic reactions. 29,31,32,[43][44][45][46][47][48][49][50][51][52][53][54] In this paper, the catalytic ability of silanetriol 5 has also been evaluated.…”